Method for controlled ink-jet spreading of polymers for the insulation and/or protection of printed circuits

ABSTRACT

Method for the controlled ink-jet spreading of polymeric material for insulation and/or protection of printed circuits, characterized in that it has at least the following steps: —carrying out at least a first bedding/bordering/border-line contour run of the circuit design, creating a line of outline/bordering design slightly raised from said printed board surface; —carrying out a subsequent filling/covering run of the outlined bordered design.

This application is a continuation of pending International PatentApplication No. PCT/IT2003/000709 filed Oct. 31, 2003, which designatesthe United States and claims priority of pending Italian PatentApplication No. UD2002A000238 filed Nov. 11, 2002.

BACKGROUND OF THE INVENTION

This invention relates to a method for the controlled ink-jet spreadingof polymers for insulation and/or protection of printed circuits,according to the preamble of the main claim.

1. Technical Field

The method finds particular and useful application in the manufacturingprocesses of printed circuit electronic cards.

2. Background Art

At present various manufacturing methods are known for printed-circuitelectronic cards.

Particular reference is made here to the cards made up of a sheet ofplastic material for example plastic reinforced with fiberglass with alayer of electrically conductive material placed on the surface such as,for example, copper, said sheets being later cut into the dimension andprofile of the desired card.

The copper surface is then subjected, using different techniques(curtain coating, sprinkling, etc.), to the deposition of the printedcircuit design.

Subsequently the exposed external surface of the copper layer isremoved, for example, with a chemical process to obtain the electronicprinted circuit.

Followed by stripping, namely the removal of the protection of thedesign previously deposited on the printed board (card).

Finally, the spreading of a protective insulating polymeric layer takesplace.

This deposition of the protective insulating polymeric layer on theprinted card or board is carried out with different techniques,generally sprinkling or curtain coating.

The spreading of the layer on a stepped/engraved surface (the level ofthe printed board is higher than the level of the plastic surface of thecard for the value of the copper layer of approximately 45 microns)involves the need to apply a substantial protective insulating layer,otherwise the corners of the circuit conductor lines might remainexposed and therefore render the card defective.

The total protection thickness implies therefore a maximum deposition of60 microns with evident material wastage.

The result of the cards obtained is not, however, always of the highestquality and precision due to the inevitable overflow of the depositedliquid material.

The overflow is furthermore inevitable because the metal is not asabsorbent as paper and despite the porosity of the plastic material itis not as high as that of the paper and for this reason it is verydifficult to obtain sharp defined outlines.

Furthermore, these insulating and protective materials are expensive.

The system for covering and protecting the cards by means of silkscreening is also known. However, this method is very slow and involvesthe use of notable material and does not allow adequate quality andprecision to be obtained.

AIM OF THE PRESENT INVENTION

The aim of the present invention is that of increasing the quality ofthe product by means of higher precision technology and furthermore, byconsiderably reducing the amount of protective and insulating polymericmaterial thus reducing significantly the manufacturing costs.

A further aim of this invention is that of reducing manufacturing timewhilst still improving the quality of the product.

SUMMARY OF THE INVENTION

The problem is solved with a method for the controlled ink-jet spreadingof polymers for insulation and/or protection of printed circuitsaccording to the characterizing part of the main claim.

Therefore, using a first border-contour deposition (bedding deposition)to contour or border or profile or delimit the deposition surfaces,before proceeding to the deposition of the layer on the surfaceconcerned in such a manner that the last one is delimited by the firstbedding deposition.

The sub-claims constitute preferred embodiments.

ADVANTAGES

Thanks to the preventive border-contour system of the design to becovered there is the great advantage of being able to add edge limitsthat allow the successive deposition layer to be contained so as toprevent overflowing out said previously deposited border-lines, thusobtaining absolute precision and a precise minimum thickness.

The result will be a product of a better final quality with aconsiderably lower amount of material used, as will be explained in thefollowing.

Naturally, the design border-contour operation, is a bedding depositionby means of a succession of linear punctiform jets, this being obtainedwith the suitable calibration of polymerization rapidity, fluidity andviscosity of the material, using an almost circular deposition sectionor in any case at least almost semicircular, with an edge heighttherefore that is normally calibrated to 15 microns. In this way thedeposit of the subsequent filling between the border-line edges will becontained without any danger of overflowing this delimiting “track”previously applied.

DESCRIPTION OF A PREFERRED EMBODIMENT

The invention is now described with the aid of the enclosed drawingsthat illustrate in a schematic cross section a portion of a printedcircuit card in the specific case concerned, in an enlarged view of twoelectric conductor lines.

All the deposits are made by means of a pixel jet system namely with theso-called inkjet system where, in contrast, ink is sprayed in pixels(punctiform droplets) onto said insulating polymeric material forprotection and/or insulation.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 represents the first deposition phase of the edge of the designof the printed board on the copper layer of the card (designborder-contour).

FIG. 2 represents the second filling phase with the protective andinsulating material of the printed board design.

FIG. 3 represents the engraving phase, namely the removal phase of thecopper layer not concerning the printed board design, exposing theunderlying support material of the card, namely the plastic reinforcedwith fiberglass.

FIG. 4 represents the stripping phase, namely the removal phase of theprotective layer placed on the surface of the design of the electricallyconductive printed board (copper) left on the surface of the plasticmaterial (plastic reinforced with fiberglass) constituting the base orsupporting body of the card.

FIG. 5 represents the repetition of the design border-contour(bordering/bedding) phase for the definitive insulating and protectivelayering/covering (first bordering/bedding step of the two-step run) ofthe salient conductor surfaces of the printed board to be insulated onthe upper part.

FIG. 5A represents a variant to the step in FIG. 5 in which, bysubsequent border-line superimpositions, a stratification of theborder-line edge is built by means of pixels from the underlying base inplastic material. In this case, the sides of the conductivecircuit-strata are already insulated preliminarily.

FIGS. 6 and 6 a represent respectively the following filling step ofcovering/filling the conductive surface between the previous beddingdesign border-contour or bordering lines, in the first case insulatingthe upper surface and in the second case providing the completeinsulation of the conductors also on their side.

FIG. 7 represents the final depositing step of the lowest plasticmaterial surface of the card between the conductors, where theinsulation and protection of the sides takes place for superficialadherence (cohesion) of the protective insulating liquid that rises onthe sides of the conductor, protecting them, until contact is made withthe upper protection.

FIG. 7A represents the same phase as FIG. 7 but, the insulation andprotection of the sides of the conductors having been carried outalready, the covering layer as protection of the base is to be appliedwith minimal thickness, or also may be completely avoided.

DETAILED DESCRIPTION OF THE DRAWINGS

With reference to the figures, it is noted that:

“P” indicates the body of the card in plastic material such as, forexample, plastic reinforced with fiberglass;

“Cu” indicates the electrically conductive copper layer placed on thesurface;

“C” indicates the copper layer left after the engraving, that definesthe conductive electronic printed circuit;

1 indicates the double line (bedding/border-line/bordering-track) thatdefines the edge or outline of the design raised by approximately 15microns;

2 indicates the deposition of the insulation and/or protective layer onthe surface of the conductive material;

3 indicates the layer of protective material applied on the plasticmaterial of the card between the conductors (border-contours).

For purely indicative purposes, the superficial dimensions of thevarious layers and materials are set out below:

-   -   card (e.g., plastic reinforced with fiberglass) “P” a few        millimeters;    -   thickness of the metallic conductor material layer (copper=Cu):        45 microns;    -   pixel height and width of protection polymer on the conductor        layer: 15 microns;    -   height of the protective polymer layer on the surface of the        plastic material: 5 microns.

Process

-   -   a) BEDDING or BORDERING or BORDER-LINE CONTOUR: the outline of        the design of the printed board on the conductor (Cu) is        deposited by means of printing with successive pixel-punctiform        jets (1), in such a way as to form a raised contour lines of        approximately 15 microns, that polymerizes immediately (FIG. 1);    -   b) FILLING: the outline is filled with a filling deposit (2), by        means of the same printer, covering of the interior surfaces        inside the previous border-line contour (1) FIG. 2;    -   c) ENGRAVING: the removal of the copper layer not interested by        the circuit design is provided, namely between the circuit        design contour (FIG. 3);    -   d) STRIPPING: the removal of the protective layer applied before        the engraving then follows, thus exposing the circuit        conductor (C) FIG. 4;    -   e) BEDDING or BORDERING or BORDER-LINE CONTOUR: application of        the design border-contour (1) along the edges of the conductive        circuit (C), FIG. 5′ 5A;    -   f) CONDUCTOR PROTECTION: spreading the protective insulation        layer (2) on the conductive circuit surface (C), between said        edges/border-lines (1), FIGS. 6′ 6A;    -   g) Final covering (3) of the non-conductive plastic card surface        (P).

In this way, it is possible to save a significant amount of materialthat is notoriously very expensive and at the same time obtain betterquality and precision, avoiding the overflow of the polymer applied.

Advantageously, the thickness of the outline deposit is within the rangeof 10 and 20 microns, preferably 15 microns.

More advantageously, the height of the printed circuit is within therange of 30-60 microns, preferably around 45 microns, for which arepeated deposit on the sides of the edges would involve three depositsto cover the sides and a fourth to project over the cover of the uppersurface.

Even more advantageously, the filling thickness of the spaces betweenthe said printed circuits is in the range of 3 to 7 microns, preferably5 microns.

The method, according to the main claim, is carried out rapidly with afast-polymerizing/hardening material so that it protrudes/raises inthickness, the polymerization/hardening being sufficiently rapid to forma barrier/border against the liquid of subsequent filling depositionlayers between them.

Advantageously the deposition of these border-contour lines is carriedout in such a way as to form barrier for the following deposition, toavoid overflowing and to contain the subsequent filling layer betweenthem.

It is evident that the profiling (border-contour) according to theprofile of the design of the electrically conductive part, that inaccordance with the characteristics of the principal claim,protrude/raise more or less from the surface, must first be polymerizedor at least partially hardened before the filling between these“border-lines” with successive subsequent filling phase, the last onebeing exactly defined between the edges of the previous border-linecontour deposition.

In this way the deposition of the filling will not be able toexceed/overflow said border contour lines limits alreadypolymerized/hardened.

1. A method for the controlled ink-jet spreading of polymeric materialfor insulation and/or protection of printed circuits, characterized inthat it includes at least the following steps: carrying out at least afirst run of the border-contour of the design to make a raisingbordering design or bedding, creating a border-line circuit designcontour/outline, slightly raised, to previously define/border saiddesign of the printed card; carrying out at least a subsequent surfacefilling/covering run of the raised contour/outline namely in the surfacedelimited by said border-line contour with the same material of thefirst run.
 2. Method for the controlled ink-jet spreading of polymericmaterial for insulation and/or protection of printed circuits accordingto claim 1, characterized in that the following steps are carried outstarting from a card including an electrically conductive metallic upperlayer (Cu) placed on a support made of plastic material (P): a) depositan immediately hardening polymeric material, linearly by points, bymeans of an ink-jet printer, to form a bordering/border-contour outlineof the circuit design to form a bordering delimitation; b) fill thedesign of said printed circuit in a subsequent covering run, so as tocover completely the interested surface design with protective material;c) subject the layer of conductive material (Cu) left exposed by theprevious covering to removal; d) remove said covering layer of saiddesign leaving exposed the surface of the conductive printed circuit (C)on the card (P); e) point-to-point deposit an insulating-protectivepolymeric material, by means of an ink-jet printer, to form theborder-line contour/outline of the surface of the printed card (C) andeventually to protect the sides; f) fill the still exposed upperconductor surface of said printed card (C) left exposed by saiddelimiting border-lines in a successive filling/covering run.
 3. Methodfor the controlled ink-jet spreading of polymeric material forinsulation and/or protection of printed circuits cards according toclaim 2, characterized in that a further run for the protection of thesurface of the card, left free by the presence of said printed circuit(P) is carried out.
 4. Method for the controlled ink-jet spreading ofpolymeric material for insulation and/or protection of printed circuitsaccording to claim 3, characterized in that said protection run of thecard surface left free by said printed circuit is carried out with thedeposition of a polymer thickness lower than 7 microns.
 5. Method forthe controlled ink-jet spreading of polymeric material ink-jet forinsulation and/or protection of printed circuits according to claim 3,characterized in that said protection run of the card surface left freeby said printed circuit is carried out with a deposition of a thicknessin the range of about 5 microns.
 6. Method for the controlled ink-jetspreading of polymeric material for insulation and/or protection ofprinted circuits according to claim 1, characterized in that theraising-thickness of said delimiting border-line contour/bordering iswithin the range of 5 to 20 microns.
 7. Method for the controlledink-jet spreading of polymeric material for insulation and/or protectionof printed circuits according to claim 1, characterized in that theraising-thickness of said delimiting border-line contour is in the rangeof about 15 microns.
 8. Method for the controlled ink-jet spreading ofpolymeric material for insulation and/or protection of printed circuitsaccording to claim 1, characterized in that said delimiting border-linecontour is carried out with more runs in order to cover the free edgesprotruding from the conductive printed circuit (C) with respect to thebase of the card (P) by means of the super-imposition of border-lines bypoints.
 9. Method for the controlled ink-jet spreading of polymericmaterial for insulation and/or protection of printed circuits accordingto claim 8, characterized in that the number of border-line contour runsis at least two, one on top of the other.
 10. Method for the controlledink-jet spreading of polymeric material for insulation and/or protectionof printed circuits according to claim 8, characterized in that thenumber of border-line contour runs is at least three, one on top of theother.
 11. Method for the controlled ink-jet spreading of polymericmaterial for insulation and/or protection of printed circuits accordingto claim 8, characterized in that the number of border-line contour runsis four, one on top of the other.
 12. Method for the controlled ink-jetspreading of polymeric material for insulation and/or protection ofprinted circuits according to claim 8, characterized in that thedeposited border-line contour material is primarily of the rapid or fastpolymerization/hardening type so as to harden at least partially by:forming a raising line of barrier at the edge of the design of theconductor/conductive-circuit; the time for the hardening of saidbarriers being lower than the required time for the followinginner-surface filling/covering run.
 13. Printed circuit card realizedusing the method according to claim 8 and including a polymericprotection strata/layer operated by ink-jet points, respectivelydifferentiated: in the raising-thickness range of about 15 microns onits sides and on the upper surface of the conductive printed circuit andin the thickness range of about 5 microns in the remaining surface(P-3); the covering-insulation layer being made up of a border-linecontour for protection, insulation in linear limitation/bordering shapeand an internal, insulating, protective, filler layer being appliedbetween said border-line contour, raising/protruding from said surface.